diff --git a/DCCEXParser.cpp b/DCCEXParser.cpp
index aaf733c..7610d45 100644
--- a/DCCEXParser.cpp
+++ b/DCCEXParser.cpp
@@ -25,6 +25,79 @@
  *  You should have received a copy of the GNU General Public License
  *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
  */
+
+/*
+List of single character OPCODEs in use for reference.
+
+When determining a new OPCODE for a new feature, refer to this list as the source of truth.
+
+Once a new OPCODE is decided upon, update this list.
+
+  Character, Usage
+  /, |EX-R| interactive commands
+  -, Remove from reminder table
+  =, |TM| configuration
+  !, Emergency stop
+  @, Reserved for future use - LCD messages to JMRI
+  #, Request number of supported cabs/locos; heartbeat
+  +, WiFi AT commands
+  ?, Reserved for future use
+  0, Track power off
+  1, Track power on
+  a, DCC accessory control
+  A,
+  b, Write CV bit on main
+  B, Write CV bit
+  c, Request current command
+  C,
+  d,
+  D, Diagnostic commands
+  e, Erase EEPROM
+  E, Store configuration in EEPROM
+  f, Loco decoder function control (deprecated)
+  F, Loco decoder function control
+  g,
+  G,
+  h,
+  H, Turnout state broadcast
+  i, Reserved for future use - Turntable object broadcast
+  I, Reserved for future use - Turntable object command and control
+  j, Throttle responses
+  J, Throttle queries
+  k, Reserved for future use - Potentially Railcom
+  K, Reserved for future use - Potentially Railcom
+  l, Loco speedbyte/function map broadcast
+  L,
+  m,
+  M, Write DCC packet
+  n,
+  N,
+  o,
+  O, Output broadcast
+  p, Broadcast power state
+  P, Write DCC packet
+  q, Sensor deactivated
+  Q, Sensor activated
+  r, Broadcast address read on programming track
+  R, Read CVs
+  s, Display status
+  S, Sensor configuration
+  t, Cab/loco update command
+  T, Turnout configuration/control
+  u, Reserved for user commands
+  U, Reserved for user commands
+  v,
+  V, Verify CVs
+  w, Write CV on main
+  W, Write CV
+  x,
+  X, Invalid command
+  y,
+  Y, Output broadcast
+  z,
+  Z, Output configuration/control
+*/
+
 #include "StringFormatter.h"
 #include "DCCEXParser.h"
 #include "DCC.h"